Electronic vibration measurement device

Abstract

The invention relates to checking the operational capability of an electronic vibration measuring device (1). In this case, the amplitude of the excitation signal (AS1, AS2) by means of which the mechanically oscillatory unit (111) is excited is varied. The check is carried out on the basis of reception signals (RS1, RS2) received from the mechanically oscillatory unit (111).

Description

Technical Field

[0001] This invention relates to the functional testing of electronic vibration measurement equipment. Background Technology

[0002] In automation technology, field devices are frequently used to register and / or influence process variables. Sensors are used to record process variables, for example, to measure fill level, limit level, flow rate, pressure, temperature, pH value, conductivity, or dielectric constant. If the focus is on the measurement of a medium within a container, then within the scope of this invention, "container" also refers to a non-closed container, such as, for example, a bucket, lake, or ocean, or a flow of water.

[0003] Applied to extreme level measurements are measuring devices, for example, those operating on the principle of electronic vibration measurement. For example, such a type of measuring device is shown in publication DE 10 2012 101 667 A1: Essentially, such a measuring device uses an electronic vibration sensor with a mechanically oscillating element, such as an oscillating fork, and an amplifier unit reverse-coupled to it (see also, for example, DE 100 50 299 A1). To determine the viscosity of a medium, frequency-phase curves are used, for example, in WO 02 / 31471 A2. Measurement of process variables based on attenuation behavior is also known (see DE 102 03 461 A1).

[0004] To convert between mechanical oscillations and electrical signals, a piezoelectric element or comparable component is mechanically coupled to an oscillating fork, enabling it to perform mechanical oscillations via an electrical excitation signal. Based on the mechanical oscillations, an electrical receiving signal is generated, the frequency of which corresponds to the frequency of the oscillation.

[0005] The received signal is tapped at the piezoelectric element, which excites mechanical oscillation. In this case, the received signal must be properly separated from the excitation signal according to existing technology. Alternatively, a separate second piezoelectric element, mechanically coupled to a mechanically oscillating element such as an oscillating fork, can serve as the output of the received signal.

[0006] The signal output of the mechanically oscillating unit used for receiving the signal is directed to an amplifier unit, the output of which is connected to the input of the electrically excited signal at the oscillating fork. If the amplifier unit provides a constant phase shift between the incoming received signal and the outgoing excited signal and has sufficient signal amplification, an oscillating circuit is formed when the frequency of the excited signal coincides with the frequency of the received signal. In such a case, the frequency depends on the phase shift predetermined by the amplifier unit (see, for example, WO 2017 / 215875 A1). On the other hand, the frequency is affected by the resonance of the oscillating fork, and thus by the possible coverage of the oscillating fork by the medium, the density or limiting level of which will be determined. Accordingly, by measuring the current frequency of the excited or received signal, it is theoretically possible to determine the possible limiting level and / or density of the medium.

[0007] When the oscillation circuit is not superimposed with external interference such as electronic vibration or electromagnetic interference fields, the electronic vibration measurement principle operates flawlessly. Electronic vibration can be generated, for example, from the operation of a processing plant, such as the operation of conveyor belts and pumps. In such cases, there is a risk that a corresponding interference signal will be superimposed on the exciter or receiver signal, thereby potentially compromising the limit level or density measurement. The problem is particularly acute when the measuring equipment is not detected to be operating unreliably within the processing plant where it is used. Depending on the region and processing plant, specific specifications or permissible procedures govern this for field equipment, limiting the ability to verify the correct operation of the field equipment; examples are the standards IEC 61508 / IEC 61511 known under the label "Safety Integrity Level (SIL)".

[0008] Different testing possibilities for measuring devices are known in the prior art.

[0009] DE 20 2005 008 627 U1 describes a measuring device having an oscillating unit and a functional test unit. The functional test unit acts on a signal received from the oscillating unit and thereby generates a test signal, which is processed by a downstream evaluation unit. In this case, the test signal corresponds to a defined measured value. Therefore, the electronic components arranged after the oscillating unit are inspected. In another electronic component inspection, EP 1 091 199 B1 provides a signal generator to generate a test signal.

[0010] DE 10 2019 131 485 A1 describes the monitoring of a coil as part of a sensor. An excitation signal is supplied to the coil, and the received signal is evaluated. Therefore, the components that are part of the transducer unit between the electrical signal and the mechanical oscillation are examined.

[0011] In WO 2017 / 097528 A1, a mechanically oscillating unit is excited to perform oscillations at different frequencies in a test mode in order to detect fault conditions from the received signal. According to DE 10 2021 129 416 A1, the processing of such a spectrum generated by frequency scanning can be performed using a neural network.

[0012] In WO 2016 / 128217 A1, the excitation of a mechanically oscillating unit is generated using a signal produced by a carrier signal having a carrier frequency and a modulating signal having a modulation frequency. The received signal consists of a carrier signal and a modulating signal, where each signal allows for the determination of process variables. Based on the phase shift between the modulating signals, attenuation is determined, which can indicate, for example, whether accumulation, corrosion, or aging effects have occurred.

[0013] In DE 10 2016 120 326 A1, the state of the oscillating circuit is derived from the time evolution of the mass of the oscillating circuit, which includes an oscillating unit and a piezoelectric element.

[0014] In WO 95 / 20749 A1, during the testing phase, an oscillating circuit consisting of an amplifier circuit and a transducer unit is disconnected. This oscillating circuit excites the oscillating unit to perform oscillations, receives its oscillations, and converts the oscillations into electrical signals. Faults are detected based on attenuation behavior, and in particular, the phase difference between the output signal of the amplifier circuit and the signal obtained from the transducer unit.

[0015] WO 2020 / 165560 A1 provides that, in test mode, a mechanically oscillating unit is excited with an excitation signal to perform oscillations at a frequency already measured in a previous measurement operation. This is done with the oscillation circuit disconnected. The functional state of the measuring device is deduced by comparing the time evolution of the amplitude of the received signal with an associated threshold.

[0016] DE 10 2004 050 494 A1 provides for exciting oscillating units in two different oscillation modes. One of these modes is unaffected by the medium, and thus enables the monitoring of sensors.

[0017] In order to detect the presence of faults according to DE 10 2005 009 580 B4, the amplitude and frequency of the oscillations are evaluated, and the results obtained under such conditions are compared with each other.

[0018] To examine the oscillating element, DE 103 18 445 A1 provides that the components of the oscillating element can be manually damped. This, in turn, generates a target mechanical fault condition.

[0019] In DE 10 2012 102 589 A1, the lack of oscillation is detected as a result of coverage or corrosion of the oscillating element by moving through a frequency range higher than that that occurs during normal operation.

[0020] To monitor the polarization of the piezoelectric element used to drive the oscillating unit, its capacitance was identified and evaluated in DE 10 2017 130 530 A1.

[0021] If material adheres to the oscillating cell, this can also lead to a fault state, since free oscillation is impossible in a practically uncovered state.

[0022] To detect the aforementioned accumulation, DE 103 28 296 A1 defines a limit value for the oscillation frequency, below which an alarm is triggered. DE 10 2009 045 204 A1 provides an amplitude curve based on the received oscillation frequency scan to detect the presence of accumulation.

[0023] DE 10 2012 101 667 A1 addresses the vibration of exogenous electrons. This is because mechanically oscillating units without excitation are only used to detect oscillations. These ideas are also expressed in DE 10 2016 124 740 A1. Summary of the Invention

[0024] The object of the present invention is to provide a measuring device, which is particularly verifiable regarding its proper operation with respect to possible interference.

[0025] The objective is achieved by a measuring device comprising an electronic vibration sensor and a control unit for determining and / or monitoring a measured variable of a medium. The electronic vibration sensor includes a mechanically oscillating unit and an amplifier unit. The mechanically oscillating unit can be excited by an electrical excitation signal having an excitation oscillation frequency and generates a received signal having a resonant frequency. The amplifier unit is designed to generate an electrical excitation signal having a defined phase shift relative to the received signal and to excite the mechanically oscillating unit using it. The control unit is designed to determine the resonant frequency and / or amplitude of the received signal and to determine the measured variable of the medium based on the determined resonant frequency and / or determined amplitude of the received signal. The control unit is designed to control the amplifier unit for checking the measuring device, such that the amplifier unit generates at least two excitation signals having equal excitation resonant frequencies and different predetermined signal strengths. The control unit is designed to determine the sensor's operational capability based on the amplitude of the received signal as a result of the different excitation signals. The amplifier unit and the mechanically oscillating unit form a closed oscillation circuit.

[0026] According to the invention, the control unit differs in that it is able to control the amplifier unit to modulate or alter the signal strength of the excitation signal for checking the measuring device. If the received signal then changes, such as as expected based on a target change in the excitation signal, this means the sensor is operating reliably. If the received signal does not change as expected, this means, for example, that the mechanically oscillating element is receiving a signal unrelated to actual resonance. That is, for example, a dominant external oscillation can exist. However, interference may also exist in the oscillation circuit formed by the mechanically oscillating unit and the amplifier unit, such as cable breakage, depolarization of the piezoelectric element as part of the transducer unit, detachment of such a piezoelectric element, or other damage in the measuring device. In such cases, the electronic vibration sensor cannot oscillate. Therefore, if the received signal does not follow the modulation of the excitation signal, a malfunction exists.

[0027] For inspection purposes, at least two excitation signals, with different signal strengths, are supplied to the mechanically oscillating unit at different times and preferably alternately or interchangeably. Thus, the signal strength of one excitation signal is greater than that of the other. Correspondingly, it is expected that, in the absence of defects, the received signals for the different excitation signals will differ from each other in amplitude relative to their respective amplitudes. In such a case, the two excitation signals have the same frequency and the same phase shift. This frequency is particularly the frequency established during measurement in the oscillation circuits of the amplifier unit and the mechanically oscillating unit, and therefore especially the resonant frequency of the mechanically oscillating unit (which, in an undisturbed state, depends essentially only on the medium and the measured variable).

[0028] This type of inspection allows for the initial identification and / or monitoring of the measured variable in the absence of media interruption. If no interference is present, the measured variable can be derived and / or monitored from each of the different received signals. This particularly relates to the assessment of the frequency of the received signals, and thus, for example, changes in the coverage of the oscillating element by the medium will manifest as measurable frequency changes. Therefore, the inspection of the measuring device can be performed without loss of measurability, and can thus be termed a field test run in parallel with the measurement.

[0029] When the mechanically oscillating unit is excited by an excitation signal, the oscillation circuits of the mechanically oscillating unit and the amplifier unit are closed in each case to realize a feedback loop.

[0030] To inspect the sensor, one option is to evaluate the received signal relative to each other. Alternatively, the received signal can be evaluated independently with reference to the measured variable. The received signal thus serves a dual function.

[0031] In the context of this invention, there are multiple options for how the excitation signal can be changed, thus utilizing abrupt or continuous (e.g., linear or sinusoidal) changes. The control unit will be designed accordingly to properly control the amplifier unit depending on the implementation. In one embodiment, two different values ​​are provided for the signal strength.

[0032] In an embodiment, switching between a first excitation signal having a first signal strength and a second excitation signal having a second signal strength is performed multiple times. Each alternation enables the ability to check the operation of the measuring device. Preferably, the alternation between the two excitation signals with different signal strengths occurs continuously during the use of the measuring device. In an embodiment, it is provided that, for example, under special application conditions, the switching of signal strength can be turned off, and therefore occurs discontinuously.

[0033] In each case, excitation is preferably performed with a signal strength over a specific time period, which is preferably chosen when transient behavior is substantially no longer present. Thus, for example, excitation is performed using a first excitation signal with a first signal strength over an initial time period, and then using a second excitation signal with a second signal strength over a second time period. Excitation is then performed again using the first excitation signal, and so on. In one embodiment, the time periods in which the first or second excitation signal is used are equal. For example, for evaluation purposes, in each case, an envelope curve is determined to obtain the near-average amplitude of the oscillations across the time periods.

[0034] In one embodiment, the control unit is designed to determine its operational capability by evaluating the envelope curve of the received signal. Preferably, in the case of an applied excitation signal, multiple oscillations of the oscillating unit are received as received signals and evaluated via the envelope curve.

[0035] The embodiment includes a control unit designed to classify a sensor as inoperable when the amplitude of the received signal does not change, does not change appropriately, or changes significantly in response to different excitation signals. In this embodiment, it is checked and signaled under given conditions: whether the received signal does not change appropriately after a change in the excitation signal.

[0036] In supplementary or alternative embodiments, the control unit is designed to classify the sensor as operational when the amplitude of the received signal changes sufficiently or significantly in response to different excitation signals. Therefore, if the desired change occurs in the received signal, the sensor is classified as operational. This is especially true when no external electronic vibrations are received that are dominant compared to the actual oscillation of the mechanically resonant unit in the oscillation circuit. It can also be assumed that there are no interruptions in the oscillation circuits of the amplifier unit and the mechanically resonant unit, i.e., especially no cable breaks, etc. Generally, faults that substantially prevent the mechanically resonant unit from performing resonance are checked and detected.

[0037] Therefore, the core of this invention is typically put into practice as follows: the signal strength of the excitation signal is modulated. If the modulation is also correspondingly recorded in the received signal, then the measuring device and all the aforementioned mechanically oscillating units and amplifier units are in order. Therefore, the measured variable can also be reliably determined or monitored from the received signal. In the case of modulation of the excitation signal's signal strength, the associated modulation will be a change in the amplitude of the received signal. However, if no modulation or inappropriate modulation is shown in the received signal, a fault exists, which prevents the mechanically oscillating unit from oscillating at its resonant frequency, which will be actually set due to the oscillation circuit and with changes in the medium. This is, for example, correspondingly transmitted as a signal.

[0038] The embodiment provides that the control unit is designed to apply a relative amplitude change of the received signal for sensor evaluation. Therefore, absolute measurement is not required. The relative amplitude change is, for example, the difference between the amplitudes of the two received signals referenced to one of two amplitudes.

[0039] The embodiment provides that the control unit is designed to provide an indication that complete coverage of the mechanically oscillating unit may exist, in a situation where the sensor would be classified as operational. In the case of complete coverage, the medium prevents the mechanically oscillating unit from oscillating. Through a transducer unit between the electrical signal and the mechanical oscillation, the excitation signal acts directly on the received signal with a small portion. In such a case, the signal depends in part on the signal strength of the excitation signal. However, this does not indicate anything about the state of the sensor—except for the transducer unit. In any case, fault-free information is obtained solely from this signal. The transducer unit, for example, consists of at least one piezoelectric element. Therefore, in this embodiment, an indication is given that the medium may also completely cover the mechanically oscillating unit.

[0040] In one embodiment, the mechanically oscillating unit is an oscillating fork, a single tooth, or a diaphragm.

[0041] Preferably, the amplifier unit is implemented to generate an excitation signal with a phase shift of, for example, 90° or 270° relative to the received signal. Alternatively, a phase shift of 270° is provided.

[0042] In the prior art, under corresponding design conditions, the control unit can determine the density and / or upper or lower limit level of the medium based on the frequency of the received signal or excitation signal, and therefore typically determines the filling level of the medium in the container as the measured variable. Frequency assessment is preferably performed when the medium is liquid.

[0043] The control unit in the embodiments is designed as an integral component of the sensor. Alternatively, a process control station or distributed server may be used as the control unit. Generally, the term "unit" in the context of this invention means, in principle, any electronic circuit or device or component suitably designed for its use. Thus, depending on the need, it can be an analog circuit for generating or processing corresponding analog signals. It can even be a (semiconductor-based) digital circuit, such as an FPGA. Attached Figure Description

[0044] The invention will now be explained in more detail with reference to the accompanying drawings, which are shown below: Figure 1 This is a schematic arrangement of the measuring device of the present invention on a container. Figure 2 It is an oscillating circuit used as a measuring device for circuits, and Figure 3 For example, in the case of an operational sensor, the curves of the excitation signal and the received signal. Detailed Implementation

[0045] In order to provide a general understanding of the measuring device 1 of the present invention, Figure 1 A schematic arrangement of measuring device 1 on container 2 is shown.

[0046] In this case, medium 3 is located in container 2, where, for example, the density of the medium needs to be determined or the change in fill level relative to the limit level needs to be recorded. Medium 3 can be a liquid or a bulk item.

[0047] Here, the measuring device 1 is connected, for example, to a remote control unit 12—e.g., a process control system. In this way, a specific measured value can be transmitted or changed and displayed. Furthermore, other information regarding the general operating status of the measuring device 1 can be transmitted. Alternatively, the control unit 12 and the sensor 11 can be integral components of the measuring device 1.

[0048] For measurement purposes, measuring device 1 is arranged laterally at the port of container 2, such as via a flange connection. In determining density, measuring device 1 needs to be arranged relative to the container height such that, at least during measurement, measuring device 1—i.e., its oscillating fork 111—is covered by the medium 3. In the case of extreme level measurements, measuring device 1 will be arranged horizontally at the height of container 2 corresponding to the extreme level to be measured.

[0049] Now based on Figure 2 The schematic circuit of the example embodiment is used to explain the operation of measuring device 1.

[0050] An electronic vibration sensor 11 is shown, comprising an oscillating fork 111 as a mechanically oscillating element and an amplifier unit 112 coupled thereto. In this configuration, the amplifier unit 112 can operate based on, for example, at least one operational amplifier. For mechanical excitation, at least a first piezoelectric element 1111 is coupled to the oscillating fork 111. In this way, when electrical excitation signals AS1, AS2 are supplied to the first piezoelectric element 1111, the oscillating fork 111 mechanically performs oscillations with corresponding frequencies fR. Additionally, the oscillating fork 111 has a second piezoelectric element 1112. In this way, the mechanical oscillation of the oscillating fork 111 generates electrically received signals RS1, RS2, the frequency of which fR corresponds to the frequency of the mechanical oscillation. Therefore, the two piezoelectric elements 1111 and 1112 together form a transducer unit.

[0051] As Figure 2 In an alternative to the illustrated embodiment, signals RS1 and RS2 are sensed and received at the first piezoelectric element 1111, thus eliminating the need for a second piezoelectric element 1112. For this purpose, signals AS1, RS1 and AS2, RS2 are separated from each other; for example, one signal is considered a current signal, and the other a voltage signal.

[0052] The signals RS1 and RS2 received from the oscillating fork 111 are directed to the input 1121 of the amplifier unit 112, and the output 1122 of the amplifier unit 112 is connected to the first piezoelectric element 1111, and thus to the input of the electrical excitation signals AS1 and AS2 at the oscillating fork 111. This creates a closed feedback loop.

[0053] Amplifier unit 112 is configured with a constant phase shift between the incoming received signals RS1 and RS2 and the emitted excitation signals AS1 and AS2. And it has a constant or controlled amplification factor. That is, the amplitude AR of the received signals RS1 and RS2 is amplified and output to the output 1122 of amplifier unit 112. By amplification and phase shifting The control is set to a constant value or predetermined by corresponding filtering, and an oscillation circuit 11 is formed accordingly, so that the frequency fR of the excitation signals AS1 and AS2 is consistent with the frequency of the received signals RS1 and RS2.

[0054] In this case, the frequency fR depends on the phase shift predetermined by the amplifier unit 112. On the other hand, the frequency fR is additionally determined by the resonant oscillation of the oscillating fork 111, which depends on whether the oscillating fork 111 may be covered by the medium 2. Accordingly, by measuring the current frequency fR of the excitation signals AS1, AS2 or the received signals RS1, RS2, the possible achievable limit levels and / or densities of the medium 2 can be determined or monitored. For this purpose, the frequency fR can be determined, for example, by the control unit 12.

[0055] Figure 3 An example of signal strength variation according to the present invention is shown. Such an example relates to an interference-free measurement device 1.

[0056] The upper row shows the envelope curves of excitation signals AS1 and AS2. It is important to note that in this case, there are significantly different signal intensities that continuously alternate, thus allowing for continuous monitoring of the measuring device's functionality. Therefore, this is an example of how monitoring by measuring device 1 occurs continuously and in parallel with the actual measurement. It is important to note that for each excitation signal AS1 and AS2, the excitation occurs alternately over an extended period of time.

[0057] The lower row shows the received signals RS1 and RS2, aligned with the excitation signals AS1 and AS2. It is important to note that a greater signal strength in the excitation signals results in a larger amplitude in the received signals. Since the modulation of the excitation signal's signal strength leads to modulation of the received signal's amplitude, it can be assumed that the sensor is functioning correctly and that there are at least no dominant interference oscillations or other defects in measuring device 1. In the case of a faulty measuring device, the amplitude will not change, or at least will not change measurably.

Claims

1. A measuring device (1) for determining and / or monitoring a measured variable of a medium (2), comprising: Electronic vibration sensor (11) and control unit (12). in, The electronic vibration sensor (11) includes a mechanically oscillating unit (111) and an amplifier unit (112). The mechanically oscillating unit (111) can be excited by an electrical excitation signal (AS1, AS2) with an excitation oscillation frequency (fE) and generate a received signal (RS) with a resonant frequency (fR). The amplifier unit (112) is designed to generate a defined phase shift relative to the received signal (RS). The electrically excited signals (AS1, AS2) are used to excite the mechanically oscillating unit (111). The control unit (12) is designed to determine the resonant frequency (fR) and / or amplitude (AR) of the received signal (RS), and to determine the measured variable of the medium (2) based on the determined resonant frequency (fE) and / or determined amplitude (AR) of the received signal (RS). The control unit (12) is designed to control the amplifier unit (112) for inspection of the measuring device (1), such that the amplifier unit (112) generates at least two excitation signals (AS1, AS2) with equal excitation oscillation frequencies (fE) and different predetermined signal strengths. The control unit (12) is designed to determine the operational capability of the sensor (11) based on the performance of the amplitude (AR) of the received signals (RS1, RS2) as a result of different excitation signals (AS1, AS2), and The amplifier unit (112) and the mechanically oscillating unit (111) form a closed oscillation circuit.

2. The measuring device according to claim 1, in, The control unit (12) is designed to control the amplifier unit (112) such that the amplifier unit (112) generates two excitation signals (AS1, AS2) with equal excitation oscillation frequencies (fE) and different predetermined signal strengths in a substantially continuous alternation.

3. The measuring device according to claim 1 or 2, in, The control unit (12) is designed to determine the operational capability by evaluating the envelope curves of the received signals (RS1, RS2).

4. The measuring device according to any one of claims 1 to 3, in, The control unit (12) is designed to classify the sensor (1) as inoperable when the amplitude (AR) of the received signal (RS1, RS2) does not change for different excitation signals (AS1, AS2).

5. The measuring device according to any one of claims 1 to 4, in, The control unit (12) is designed to classify the sensor (1) as operational when the amplitude (AR) of the received signal (RS1, RS2) changes in response to different excitation signals (AS1, AS2).

6. The measuring device according to any one of claims 1 to 5, in, The control unit (12) is designed to apply relative amplitude changes of the received signals (RS1, RS1) to evaluate the sensor (11).

7. The measuring device according to any one of claims 1 to 6, in, The control unit (12) is designed to give an indication that full coverage of the mechanically oscillating unit (111) is possible in cases where the sensor (1) will be classified as operational.

8. The measuring device according to any one of claims 1 to 7, in, The amplifier unit (112) is designed to produce a phase shift of 90° or 270°. The excitation signals (AS1, AS2) of ).

9. The measuring device according to any one of claims 1 to 8, in, The mechanically oscillating unit (111) is an oscillating fork, a single tooth, or a diaphragm.

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